The overall objective of this proposal is to study the neurobiology and neuropharmacology of inhibitory synaptic transmission in the mammalian central nervous system. Our studies will be directed toward defining some of the cellular mechanisms of GABAnergic neurotransmission. Major goals are to: 1. define the role(s) of neuroactive butyrolactones and chemically related compounds in modulating the electrophysiological effects of GABA; 2. identify possible modulatory effects of GABA on intracellular pH and free calcium concentration; and 3. elucidate some characteristics of presynaptic GABA release. Our experiments will be done with hippocampal neurons cultured from neonatal rats and will utilize whole cell recording techniques in either current-clamp or voltage-clamp mode. The results of these experiments should improve our understanding of the mechanisms used by the brain to limit the spread of electrical activity and may help in the development of better drugs for the treatment of epilepsy and other neurological disorders. Specifically, we plan to: 1a.Examine many of the compounds described in Projects 1 and 2 to ascertain whether they are receptor agonists (diminish GABA-mediated chloride currents), inverse agonists (enhance GABA-mediated chloride currents), antagonists (block agonists and inverse agonists without having a direct effect on GABA currents), or inactive (at the GABA receptor). 1b.Examine interactions between butyrolactones and other compounds known to act at the GABA(A) receptor (GABA(A) agonists, benzodiazepines, and barbiturates). 1c.Determine whether butyrolactones up- or down-regulate GABA(A) receptors in cultured hippocampal neurons. 2.Determine whether GABA can directly alter the pH or intracellular calcium of cultured hippocampal neurons. 3a.Physiologically estimate the concentration of GABA actually released at inhibitory synapses. 3b.Determine whether GABA release in the central nervous system is always dependent on calcium entry.